Effect of Chitin Modification on the Sorption Efficiency of Reactive Black 5 Dye

Around 7.10(5) tons of dyes are produced annually to supply for the needs of the global textile, tanning and paper industry. Due to the low susceptibility of some materials to dyeing process and high solubility of dyes, up to 50% get into sewage, about 15% of which goes to the natural environment. Colored substances are mostly difficult to biodegrade, so decolorization of wastewater using biological methods used on conventional wastewater treatment plants is not effective. One of the most effective, cheap and environmentally friendly methods of removing dyes from wastewater is the adsorption process. However, the practical application of this process encounters a number of limitations, mainly due to the high cost of commercial sorbents and difficulties in their regeneration. Therefore, many studies focus on the search for cheap and effective sorbents. Recently, chitin, which is one of the most widespread biopolymers in nature, is becoming more and more popular among sorbents. According to literature data, the annual global production of chitin by living organisms reaches up to 10(11) tons and 120,000-200,000 tons of chitin are obtained in the world from the waste of marine invertebrates processing annually. However, not all kinds of waste from various industry sectors are characterized by a high sorption capacity for dyes. That encourages seeking various methods of modifying potential sorbents to improve this ability. The study investigated the possibility of increasing the adsorption capacity of chitin in relation to the RB5 dye by initial modification of the sorbent. Modifying factors such as ultrasound, microwaves, magnetic field and ozone were used. Due to appropriate modification, the maximum sorption capacity of chitin in relation to the anionic dye Reactive Black 5 has changed. It was found that the effectiveness of the RB5 dye on chitin was influenced by the initial concentration of the solution and the type of modifying agent. Among the tested sorbents, the highest sorption capacity of 38.02 mg/dm(3) was obtained for chitin modified with magnetic field at an induction of 15 mT. The efficiency of removing the anionic dye on this sorbent was higher than the maximum sorption capacity of unmodified chitin by 25%. In order to determine the exact effect of the magnetic field on chitin, additional and more detailed studies would have to be carried out. The lowest sorption capacity was obtained for chitin treated with ozone in the amount of 2 g of O-3 , where the result of 13.17 mg/dm(3) was obtained. Ozonation affected negatively the sorption capacity of chitin by its partial depolymerisation and disruption of bonds, such as hydrogen bonds, responsible for the sorption of impurities in the form of anions.